OBJECTIVES: Current European Society of Cardiology Guidelines recommend dual antiplatelet therapy for 12 months for all patients with acute coronary syndrome (ACS). The variations in antiplatelet treatment patterns at 6 months following hospital discharge were assessed in patients with unstable angina (UA), non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation MI (STEMI) undergoing percutaneous intervention (PCI). METHODS: A prospective, observational registry of 11 European countries grouped into 6 clusters recruited acute coronary syndrome (ACS) patients undergoing PCI from 2008-2009.  Interventional cardiologists collected data from ACS events up to hospital discharge, and primary care physicians and cardiologists collected 6-month data. RESULTS: Of 3042 eligible patients at baseline, 2964 patients (97%) had 6 month data; 51% of patients presented with STEMI and 49% with UA/NSTEMI.  The median age was 62 yrs.  At 6 months following hospital discharge, the percentage of UA/NSTEMI and STEMI patients using clopidogrel, respectively, was 70% and 40% in the Czech Republic, 84% and 89% in Germany, 98% and 99% in Greece, 78% and 81% in the Nordic countries, 93% and 94% in Austria and Hungary, and 81% and 88% in Belgium and the Netherlands.  The percentage of UA/NSTEMI and STEMI patients taking aspirin, respectively, was 98% and 99% in the Czech Republic, 89% and 90% in Germany, 97% and 100% in Greece, 95% and 93% in the Nordic countries, 94% and 96% in Austria and Hungary, and 91% and 94% in Belgium and the Netherlands.  CONCLUSIONS: Use of clopidogrel varied considerably between European countries at 6 months after discharge, whereas the majority (≥90%) of patients continued to use aspirin.  Results suggest that both physician and patient education on continuing dual antiplatelet therapy may be needed.